Mars, is one of the planetary bodies where water flowed and where it may transiently flow today under certain conditions. Many martian paleodrainage systems and well-preserved fluvial and lacustrine deposits have been recognized and studied in the last two decades (see further reading). Widespread dendritic valley networks and the presence of extensive fluvial features on ancient martian terrains suggest that a relatively “warm and wet” climate was prevalent early in the planet’s history (about 3.7 Ga). This is in stark contrast with the hyper-arid, extremely cold climate that is thought to have persisted from 3 Ga until the present (Amazonian Era). The subject of this post is Moa Valles [Salese et al., 2016], which is a 2 billion year old paleodrainage system (Figure 1) that is nearly 300 km long and is carved into ancient highland terrains of Tempe Terra in the northern hemisphere of Mars. Understanding the origin and evolution of this type of complex and interconnected paleo-fluvio-lacustrine system is critical for understanding the early martian climate.

Figure 1: The upper panel shows the THEMIS-VIS daytime mosaic of Moa Vallis system.The lower panel is a line drawing showing the channel system in blue lines, red dotted lines represent wrinkle ridges, the drainage basin is delimited in grey, and fan-shaped and deltaic deposits in orange. The total mapped length of the channel as shown here is ~325 km, and the flow direction is towards the east.

Gale crater, the site of the currently active Mars Science Laboratory (MSL) or Curiosity Rover mission, is a ~154-km-diameter impact crater formed during the Late Noachian/Early Hesperian at the dichotomy boundary on Mars (Cabrol et al., 1999; Anderson and Bell III, 2010; Wray, 2013). The northern floor and rim of Gale are ~1–2 km lower in elevation than its southern floor and rim, and the crater shows a layered central mound named Aeolis Mons, which is 100 km wide, extends over an area of 6000 km2, and is up to 5 km in height (Malin and Edgett, 2000).

Image 1: Details of the lobate features, arcuate ridges and terminal moraines in the central mound of Gale.

Post by G. de Villiers, Faculty of Geoscience, Utrecht University.

Fan-shaped deposits have been identified on the surface of Mars (Image 1). These sediment bodies often occur within impact craters and, specifically in the cases of fan deltas, suggests that these craters were once lakes early in Martian history. Fan delta morphologies are indicative of upstream (e.g. flow discharge and sediment properties) and downstream (e.g. basin characteristics) parameters, from which the hydrological conditions at the time of formation can be inferred (e.g. Kleinhans et al. 2010).

A group of Martian craters formerly contained lakes, some of which overtopped and breached the crater rims to cause flooding and channel erosion.

Image 1: View of Morella Crater and the complex of Elaver Vallis channels eroded by floodwaters released when the crater rim was breached. The distal reaches of Elaver Vallis were obliterated by the southward expansion of Ganges Chasma, which is 5 km deep. The chasma as seen today did not exist during the Elaver flood, otherwise high groundwater pressures would have been relieved by breakouts in the walls and floor of the chasma [graphic is a mosaic of THEMIS daytime infrared (IR) images].

There is much morphologic evidence that there was flowing water on the surface of Mars early in its history. Such evidence includes fluvial channels and valleys, often termed valley networks, (e.g., Pieri, 1980; Irwin, 2005a; Fassett and Head, 2008a) as well as paleolake basins that are fed by these valley networks (e.g., Goldspiel and Squyres, 1991; Cabrol and Grin, 1999, 2001; Irwin et al., 2005b; Fassett and Head, 2005, 2008b).

Image 1. Exposed layered deposit of probable lacustrine origin within an open-basin lake (-27.7°N, 76.1°E). Inset image (indicated by red box in main image) shows detailed layering within the exposed deposit. Main image is from the Context Camera (CTX) instrument (image number B02_010338_1518_XI_28S282W; ~5 m/pixel), and inset image is from the High Resolution Imaging Science Experiment (HiRISE) instrument (image number PSP_010338_1525; ~50 cm/pixel).

The hypothesis of ancient Martian standing bodies of water, which might have occupied the lowlands of the northern hemisphere and which might have existed in local- to regional-scale paleolakes once in Martian history, is one of the most important subjects of ongoing discussion in Mars research (e.g., Parker et al., 1989, 1993; Head et al., 1999; Cabrol and Grin, 1999, 2001; Clifford and Parker, 2001; Kreslavsky and Head, 2002; Carr and Head, 2003; Ghatan and Zimbelman, 2006; Di Achille and Hynek, 2010; Mouginot et al., 2012). The case for large standing bodies of liquid water, including lakes, seas and oceans, is attributed to a complex hydrologic cycle that may have once existed on Mars in the Noachian (>3.7 Ga) and perhaps also in the Hesperian (>3.1 Ga).

Polygons are some of the most common features at high latitudes on Mars and have been observed by both lander and orbiting spacecraft. They range in size from 2 m all the way up to 10 km and different formation mechanisms have been proposed that include thermal contraction, desiccation, volcanic, and tectonic processes (Buczkowski and McGill, 2002; Levy et al., 2009; Mangold, 2005; Marchant and Head, 2007; McGill and Hills, 1992; Yoshikawa, 2003).

Crater floor polygons have diameters ranging from 15 to 350 m (Image 1). Although, morphologically they resemble both terrestrial thermal contraction polygons and desiccation cracks, their size distribution is significantly larger than thermal contraction polygons that are ubiquitous in the Martian high latitudes.

Image 1. Typical crater floor polygons. [A] CTX (a 6 meter/pixel camera onboard the Mars Reconnaissance Orbiter, P16_007372_2474).of a 14 km‐sized impact crater (location: 67.2°N, 47.8°E). [B] Close-up from the same image. Two distinct size groups can be seen: A large 70-350 m sized polygons with an average polygon diameter of 120 m and mainly orthogonal trough intersection, and a smaller group, not always present, ranging in size from 5 to 20 m. [C] High resolution HiRISE (a telescopic camera with an impressive 25 cm/pixel resolution onboard the same spacecraft as the CTX, PSP_007372_2247) sub-image for the same crater of a 100 m‐wide polygon with a 6-8 m-wide, frost‐filled troughs surrounding it. Secondary troughs within the larger features form polygons with an average diameter of 10 m. These embedded features are probably periglacial thermal contraction polygons.

Surface conditions on Titan are near the triple point of methane, suggesting a methane-based hydrologic cycle which may incorporate solid, liquid, and gaseous phases. Albedo patterns on Titan’s surface evident in early Earth-based observations were interpreted as dark hydrocarbon liquids in topographic lows between exposures of bright water-ice bedrock (Lorenz and Lunine, 2005; Smith et al., 1996).

Initial data from the Cassini-Huygens mission detected more than 75 radar dark patches in the northern portion of a 6,000 km long swath of the surface (Image 1). These features measured from 3 km to in excess of 70km across. The backscatter of some of the dark patches had much lower reflectivity than previously imaged areas on Titan, including the radar-dark sand dunes observed near Titan’s equator (Sept. 2007 PGWG featured image).

mage 1: Radar imaging data from a Cassini flyby. The intensity in this false-coloured image is proportional to how much radar brightness is returned. The lakes, darker than the surrounding terrain, are emphasized by tinting regions of low backscatter in blue. Radar-brighter regions are shown in tan. The strip of radar imagery is foreshortened to simulate an oblique view of the highest latitude region, seen from a point to its west. This radar image was acquired by the Cassini radar instrument in synthetic aperture mode on July 22, 2006. The image is centered near 80° north, 35° west and is about 140 kilometers (84 miles) across. Smallest details in this image are about 500 meters (1,640 feet) across. Credit: NASA/JPL

Alluvial fans are sedimentary deposits that accumulate where streams emerge from steep mountain watersheds onto low-gradient plains. Flooding in the upland area transports a wide range of sediment sizes, and when the stream emerges onto the plain, it no longer has the power to transport the same quantity and size of sediment. Only part of an alluvial fan’s width is active at any one time, but as sediment accumulates in that area, flows will move to steeper routes elsewhere on the fan surface. Sediment may be delivered through normal stream flows or debris flows, which are concentrated slurries of sediment and water. Alluvial fans that were formed mostly by debris flows are usually steeper than their stream-dominated counterparts.

The Nili Fossae region of Mars has a diversity of minerals that include mafics and phyllosilicates. The mineral assemblage suggests widespread liquid water activity and a variety of alteration processes from surface weathering to hydrothermal processes (Mangold et al., 2007).